On 2/19/2020 2:11 AM, Leon Romanovsky wrote:
On Tue, Feb 18, 2020 at 12:11:47PM -0500, Dennis Dalessandro wrote:
On 2/18/2020 9:04 AM, Leon Romanovsky wrote:
On Fri, Feb 14, 2020 at 01:13:53PM -0500, Dennis Dalessandro wrote:
Was there any discussion on the upgrade scenario for existing deployments as
far as device-rename changing node descriptions?
If someone is running an older version of rdma-core they are going to have a
certain set of node descriptions for each node. This could be in logs, or
configuration databases, who knows what. Now if they upgrade to a new
version of rdma-core their node descriptions all automatically change out
from under them by default.
Of course the admin could disable the rename prior to upgrade and as Leon
pointed out previously the upgrade won't remove the disablement file. The
problem is they would have to know to do that ahead of time.
Dennis,
It was discussed and the conclusion was that most if not all users are
using one of two upgrade and strategy.
Do you have a pointer to a thread I can read, I apparently missed it?
First, we started to talk about it even before patches were sent.
See this summary from LPC 2017:
* the sysadmin will be able to disable this for "backward support"
https://lore.kernel.org/linux-rdma/20170917125603.GA5788@mtr-leonro.local/
Second, during the submission too, just need to continue to google it :)
So it was discussed at a meeting 2 years ago that not everyone was at, I
certainly wasn't, and you summarized with:
* predictable or persistent device names?
* need to be able to rename a device
That's not very helpful. Even Jason's presentation that is linked there
does not address the down side to the node rename especially as far as
the impact to node description is concerned.
I have looked at the original submission and again I don't see any
mention of the node description problem. Just an admission that the
names are harder to read and not what everyone is used to but being
consistent in scripts is much more important [1].
I'd have to say the script angle is far less important than
configuration files for thousands of nodes of a large deployment being
obsoleted without an end user's knowledge beforehand.
First option is to rely on distro and every distro behaves differently
in such cases, some of them won't change anything till their last user
dies :) and others more dynamic with more up-to-date packages already
adopted our default.
This is the issue I see. The problem is when the distro doesn't know any
better and pulls in a new rdma-core and breaks things unintentionally. Up to
date is good, but up to date that brings with it what is essentially an ABI
breakage is not.
ABI breakage is a strong word, luckily enough it is not defined at all.
We never considered dmesg prints, device names, device ordering as an
ABI. You can't rely on debug features too, they can disappear too.
Agree, it is a strong word and we can call it what you want. The point
is you should be able to rely on the node description not being changed
out from under you unnecessarily though. We aren't talking about a debug
feature here but a core feature to real world deployments.
Could you envision a patch to a user space library that just changes a
devices hostname to something that was HW specific because it makes
scripting easier? I contend that in some cases the node description
remaining constant is just as important.
So the bottom line, the expectation that distro should fix all broken
software before enabling device renaming and their bugs are not excuse
to declare ABI breakage.
Again, call it what you want, but you can't deny this change to force
the rename by default has not broken things. For the record I'm not even
talking about PSM2 here. There are other, more far reaching implications.
Second option is to use numerous OFED stacks, which are expected to
provide full upgrade to all components which will work smoothly.
Yeah I'm sure OFED will handle things for themselves.
At the end, OFED stacks behave like "mini-distros", so if they manage to
handle it, distro should do the same.
The difference there is to the distro the RDMA sub system is but one
small part. To OFED it is the sole focus. So I expect OFED stacks to be
more agile at handling this sort of thing.
[1]https://patchwork.kernel.org/patch/10870445/
-Denny
